Function discards any whitespace characters (as determined by std::isspace()) until first non-whitespace character is found. Then it takes as many characters as possible to form a valid floating point representation and converts them to floating point value. The valid floating point value can be one of the following:

decimal floating point expression. It consists of the following parts:

(optional) plus or minus sign

nonempty sequence of decimal digits optionally containing decimal point character (as determined by the current C locale) (defines significand)

(optional)e or E followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent)

binary floating point expression. It consists of the following parts:

(optional) plus or minus sign

0x or 0X

nonempty sequence of hexadecimal digits optionally containing a decimal point character (as determined by the current C locale) (defines significand)

(optional)p or P followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent)

infinity expression. It consists of the following parts:

(optional) plus or minus sign

INF or INFINITY ignoring case

not-a-number expression. It consists of the following parts:

(optional) plus or minus sign

NAN or NAN(char_sequence) ignoring case of the NAN part. char_sequence can only contain alphanumeric characters. The result is a quiet NaN floating point value.

any other expression that may be accepted by the currently installed C locale

The functions sets the pointer pointed to by str_end to point to the character past the last character interpreted. If str_end is NULL, it is ignored.

Contents

Floating point value corresponding to the contents of str on success. If the converted value falls out of range of corresponding return type, range error occurs and HUGE_VAL, HUGE_VALF or HUGE_VALL is returned. If no conversion can be performed, ​0​ is returned and *str_end is set to str.